Barrier client protocol¶

QEMU’s input-barrier device implements the client end of the KVM (Keyboard-Video-Mouse) software Barrier.

This document briefly describes the protocol as we implement it.

Message format¶

Message format between the server and client is in two parts:

the payload length, a 32bit integer in network endianness
the payload

The payload starts with a 4byte string (without NUL) which is the command. The first command between the server and the client is the only command not encoded on 4 bytes (“Barrier”). The remaining part of the payload is decoded according to the command.

Protocol Description¶

This comes from barrier/src/lib/barrier/protocol_types.h.

barrierCmdHello “Barrier”¶

Direction:

server -> client

Parameters:

{ int16_t minor, int16_t major }

Description:

Say hello to client

minor = protocol major version number supported by server

major = protocol minor version number supported by server

barrierCmdHelloBack “Barrier”¶

Direction:

client ->server

Parameters:

{ int16_t minor, int16_t major, char *name}

Description:

Respond to hello from server

minor = protocol major version number supported by client

major = protocol minor version number supported by client

name = client name

barrierCmdDInfo “DINF”¶

Direction:: client ->server
Parameters:: { int16_t x_origin, int16_t y_origin, int16_t width, int16_t height, int16_t x, int16_t y}
Description:: The client screen must send this message in response to the barrierCmdQInfo message. It must also send this message when the screen’s resolution changes. In this case, the client screen should ignore any barrierCmdDMouseMove messages until it receives a barrierCmdCInfoAck in order to prevent attempts to move the mouse off the new screen area.

barrierCmdCNoop “CNOP”¶

Direction:: client -> server
Parameters:: None
Description:: No operation

barrierCmdCClose “CBYE”¶

Direction:: server -> client
Parameters:: None
Description:: Close connection

barrierCmdCEnter “CINN”¶

Direction:

server -> client

Parameters:

{ int16_t x, int16_t y, int32_t seq, int16_t modifier }

Description:

Enter screen.

x, y = entering screen absolute coordinates

seq = sequence number, which is used to order messages between screens. the secondary screen must return this number with some messages

modifier = modifier key mask. this will have bits set for each toggle modifier key that is activated on entry to the screen. the secondary screen should adjust its toggle modifiers to reflect that state.

barrierCmdCLeave “COUT”¶

Direction:: server -> client
Parameters:: None
Description:: Leaving screen. the secondary screen should send clipboard data in response to this message for those clipboards that it has grabbed (i.e. has sent a barrierCmdCClipboard for and has not received a barrierCmdCClipboard for with a greater sequence number) and that were grabbed or have changed since the last leave.

barrierCmdCClipboard “CCLP”¶

Direction:

server -> client

Parameters:

{ int8_t id, int32_t seq }

Description:

Grab clipboard. Sent by screen when some other app on that screen grabs a clipboard.

id = the clipboard identifier

seq = sequence number. Client must use the sequence number passed in the most recent barrierCmdCEnter. the server always sends 0.

barrierCmdCScreenSaver “CSEC”¶

Direction:

server -> client

Parameters:

{ int8_t started }

Description:

Screensaver change.

started = Screensaver on primary has started (1) or closed (0)

barrierCmdCResetOptions “CROP”¶

Direction:: server -> client
Parameters:: None
Description:: Reset options. Client should reset all of its options to their defaults.

barrierCmdCInfoAck “CIAK”¶

Direction:: server -> client
Parameters:: None
Description:: Resolution change acknowledgment. Sent by server in response to a client screen’s barrierCmdDInfo. This is sent for every barrierCmdDInfo, whether or not the server had sent a barrierCmdQInfo.

barrierCmdCKeepAlive “CALV”¶

Direction:: server -> client
Parameters:: None
Description:: Keep connection alive. Sent by the server periodically to verify that connections are still up and running. clients must reply in kind on receipt. if the server gets an error sending the message or does not receive a reply within a reasonable time then the server disconnects the client. if the client doesn’t receive these (or any message) periodically then it should disconnect from the server. the appropriate interval is defined by an option.

barrierCmdDKeyDown “DKDN”¶

Direction:

server -> client

Parameters:

{ int16_t keyid, int16_t modifier [,int16_t button] }

Description:

Key pressed.

keyid = X11 key id

modified = modified mask

button = X11 Xkb keycode (optional)

barrierCmdDKeyRepeat “DKRP”¶

Direction:

server -> client

Parameters:

{ int16_t keyid, int16_t modifier, int16_t repeat [,int16_t button] }

Description:

Key auto-repeat.

keyid = X11 key id

modified = modified mask

repeat = number of repeats

button = X11 Xkb keycode (optional)

barrierCmdDKeyUp “DKUP”¶

Direction:

server -> client

Parameters:

{ int16_t keyid, int16_t modifier [,int16_t button] }

Description:

Key released.

keyid = X11 key id

modified = modified mask

button = X11 Xkb keycode (optional)

barrierCmdDMouseDown “DMDN”¶

Direction:

server -> client

Parameters:

{ int8_t button }

Description:

Mouse button pressed.

button = button id

barrierCmdDMouseUp “DMUP”¶

Direction:

server -> client

Parameters:

{ int8_t button }

Description:

Mouse button release.

button = button id

barrierCmdDMouseMove “DMMV”¶

Direction:

server -> client

Parameters:

{ int16_t x, int16_t y }

Description:

Absolute mouse moved.

x, y = absolute screen coordinates

barrierCmdDMouseRelMove “DMRM”¶

Direction:

server -> client

Parameters:

{ int16_t x, int16_t y }

Description:

Relative mouse moved.

x, y = r relative screen coordinates

barrierCmdDMouseWheel “DMWM”¶

Direction:

server -> client

Parameters:

{ int16_t x , int16_t y } or { int16_t y }

Description:

Mouse scroll. The delta should be +120 for one tick forward (away from the user) or right and -120 for one tick backward (toward the user) or left.

x = x delta

y = y delta

barrierCmdDClipboard “DCLP”¶

Direction:

server -> client

Parameters:

{ int8_t id, int32_t seq, int8_t mark, char *data }

Description:

Clipboard data.

id = clipboard id

seq = sequence number. The sequence number is 0 when sent by the server. Client screens should use the/ sequence number from the most recent barrierCmdCEnter.

barrierCmdDSetOptions “DSOP”¶

Direction:

server -> client

Parameters:

{ int32 t nb, { int32_t id, int32_t val }[] }

Description:

Set options. Client should set the given option/value pairs.

nb = numbers of { id, val } entries

id = option id

val = option new value

barrierCmdDFileTransfer “DFTR”¶

Direction:

server -> client

Parameters:

{ int8_t mark, char *content }

Description:

Transfer file data.

mark = 0 means the content followed is the file size
1 means the content followed is the chunk data
2 means the file transfer is finished

barrierCmdDDragInfo “DDRG”¶

Direction:

server -> client

Parameters:

{ int16_t nb, char *content }

Description:

Drag information.

nb = number of dragging objects

content = object’s directory

barrierCmdQInfo “QINF”¶

Direction:

server -> client

Parameters:

None

Description:

Query screen info

Client should reply with a barrierCmdDInfo

barrierCmdEIncompatible “EICV”¶

Direction:

server -> client

Parameters:

{ int16_t nb, major *minor }

Description:

Incompatible version.

major = major version

minor = minor version

barrierCmdEBusy “EBSY”¶

Direction:: server -> client
Parameters:: None
Description:: Name provided when connecting is already in use.

barrierCmdEUnknown “EUNK”¶

Direction:: server -> client
Parameters:: None
Description:: Unknown client. Name provided when connecting is not in primary’s screen configuration map.

barrierCmdEBad “EBAD”¶

Direction:: server -> client
Parameters:: None
Description:: Protocol violation. Server should disconnect after sending this message.